Billy Sanders

Cardiomyocyte intracellular calcium and cardiac dysfunction after burn trauma.

Objective To examine the effects of pharmacologic agents designed to limit burn-mediated calcium overload on cardiomyocyte [Ca2+] and cardiac contractile function. Design Experimental, comparative study. Setting Cellular biology and physiology laboratory. Subjects Adult Sprague Dawley rats. Interventions Rats were given third-degree burn injury over 40% of the total body surface area, were fluid resuscitated, and then were divided randomly to receive one of five treatments: vehicle (normal saline); amiloride (50 mg/kg) to inhibit H+-Na+ exchange and subsequent Na+-Ca2+ exchange; dantrolene (10 mg/kg, 30 mins, 6 and 22 hrs postburn) to inhibit sarcoplasmic reticulum Ca2+ release; diltiazem (10 mg/kg given over first 6 hrs postburn); or amlodipine (0.07 mg/kg, 24 hrs preburn and 30 mins postburn) to block calcium slow channels. Appropriate controls (sham burns given the appropriate pharmacologic agent) were included in each group. Twenty-four hrs postburn, left ventricular function (Langendorff), cardiomyocyte [Ca2+]i and [Na+]i measured by fura-2-AM or sodium-binding benzofurzan isophthalate loading of cardiomyocytes, and myocyte secretion of tumor necrosis factor-&agr; (enzyme-linked immunosorbent assay) were assessed in shams and burns from each experimental group. This time point was selected based on our previous work confirming maximal ventricular contractile defects and maximal cytokine secretion 24 hrs postburn. Measurements and Main Results Burn trauma increased myocyte [Ca2+]i and [Na+]i, promoted tumor necrosis factor-&agr; secretion by cardiomyocytes, and impaired left ventricular function. All pharmacologic agents reduced the burn-mediated Ca2+/Na+ accumulation in cardiomyocytes and ablated burn-mediated tumor necrosis factor-&agr; secretion by myocytes; in contrast, dantrolene and amiloride provided significantly greater cardioprotection than pharmacologic agents that specifically targeted Ca2+ slow channels (diltiazem and amlodipine). Conclusion Our data suggest that the calcium antagonists used in this study provide cardioprotection by modulating several aspects of the overall inflammatory cascade rather than solely limiting cardiomyocyte accumulation of calcium.

Effects of burn serum on myocardial inflammation and function.

Large cutaneous burns are clearly recognized to produce acute myocardial contractile dysfunction. This study used a model of burn serum challenge in either primary cardiomyocyte cultures or isolated perfused hearts to examine several aspects of burn-serum-related contractile dysfunction as well as myocardial inflammatory responses. Despite the absence of detectable LPS in burn serum, pretreating isolated cells or perfused hearts with recombinant bactericidal permeability-increasing protein (rBPI21) prevented both the inflammatory cytokine cascade and the cardiac contractile dysfunction induced by burn serum treatment of myocytes or ventricular muscle preparations. Our finding that anti-TNF strategies applied to isolated myocytes or hearts before burn serum challenge prevented myocardial inflammation and contractile dysfunction suggested that LPS or LPS-like factors may require the action of second messengers such as TNF-α and IL-1β to mediate LPS-related myocardial depressant effects. Our finding that experimental approaches neutralizing circulating LPS provided cardioprotection suggested that bacterial endotoxin or LPS-like molecules contribute, in part, to burn-related myocardial contractile dysfunction.

Myocardial Inflammatory Responses to Sepsis Complicated by Previous Burn Injury

BACKGROUND It is generally accepted that an initial injury such as burn trauma alters immune function such that a second insult increases the morbidity and mortality over that observed with each individual insult. We have shown previously that either burn trauma or sepsis promotes cardiomyocyte secretion of TNF-alpha and IL-1beta, cytokines that have been shown to produce myocardial contractile dysfunction. This study determined whether a previous burn injury (given eight days prior to sepsis) (1) provides a preconditioning phenomenon, decreasing inflammatory responses to a second insult or (2) exacerbates inflammatory response observed with either injury alone. METHODS Anesthetized Sprague-Dawley rats were given either burn injury over 40% total body surface area, sepsis alone (intratracheal S. pneumoniae, 4 x 10(6) colony forming units) or sepsis eight days after burn; all rats received lactated Ringers solution. Hearts harvested 24 h after onset of sepsis alone or sepsis plus eight-day burn were used to (1) isolate cardiomyocytes (collagenase) or (2) assess contractile function (Langendorff). Cardiomyocytes loaded with 2 microg/mL Fura-2AM or sodium-binding benzofuran isophthalate were used to measure intracellular calcium and sodium concentrations (Nikon inverted microscope, Grooney optics, InCyt Im2 Fluorescence Imaging System). Additional cardiomyocytes were used to measure myocyte-secreted TNFalpha, IL-1, IL-6, IL-10 (pg/ml, ELISA). RESULTS Either burn trauma alone or sepsis alone promoted TNF-alpha, IL-1beta, nitric oxide, IL6 and IL-10 secretion by cardiomyocytes (p < 0.05). Producing aspiration-related pneumonia eight days postburn produced myocardial pro- and anti-inflammatory responses and increased myocyte Ca2+/Na+ concentrations to a significantly greater degree than the responses observed after either insult alone. CONCLUSIONS A previous burn injury alters myocardial inflammatory responses, predisposing the burn-injured subject to exaggerated inflammation, which correlates with greater myocardial dysfunction.